Geochemical Characteristics and SHRIMP Zircon U-Pb Age of the Putaishan Granite Porphyry and Their Geological Implications

The Putaishan granite porphyry is an alkali-rich intrusion in Heqin, Yunnan province. In this study, we conducted whole-rock major and trace element analyses and zircon SHRIMP U-Pb dating of the Putaishan granite porphyry. The Putaishan granite porphyry has high K2O and Na2O+K2O contents, low Mg# (0.20-0.32), low magma temperature, oxygen fugacity and shallow melting depth. Zircon SHRIMP U-Pb dating yielded a crystallization age of ca.34 Ma, indicating that the Putaishan intrusion was emplaced in the Eocene epoch. Combined the obtained ages (218-541 Ma) of zircon cores and previous Pb isotope results on alkali intrusions in this region, we propose that the Cenozoic oxidized alkali-rich intrusions in the Ailaoshan-Jinshajiang belt are possibly resulted from partial melting of carbonated metasomatized mantle peridotite beneath the ancient subduction zone during the divergent strike-slip movements of the Ailaoshan-Jinshajiang faults. Meanwhile, the extension and shearing caused by the collision between the India and the Eura-Asia block in the Ailaoshan-Jinshajiang region triggered the upwelled mantle that supplied heat for dehydration of the deep crust which produced crust-derived reduced fluids, and the decompression melting of the lower crustal materials with the aid of such reductive fluids resulted in the formation of the Putaishan granite porphyry. © 2020, Science Press. All right reserved.